There are continuing goals in semiconductor fabrication to reduce the number of masks or steps needed to fabricate semiconductor devices, e.g., memory cell devices such as DRAMs. Likewise, there is a continuing goal to shrink the size of such devices thereby maximizing the density of the resulting chip or die. Lastly, there is a desire to provide such devices that perform consistently.
There has been some recent interest in the use of carbon nanotubes due to their remarkable properties. Researchers have found carbon nanotubes to be stronger and tougher than steel, capable of carrying higher currents than either copper or superconductors, and able to form transistors a few nanometers across. In addition, nanotubes have high thermal conductivity and are stable at high temperatures. E. Lerner, “Putting Nanotubes to Work,” The Industrial Physicist, pp. 22–25 (Dec. 1999). Further, carbon nanotubes may have a consistent resistance (predicted to be about 6.0 kilohms) regardless of the length of the tube due to the intrinsic characteristics of ballistic transport in such nanotubes. A. Kasumov, “Supercurrents Through Single-Walled Carbon Nanotubes,” Science, 284, 1508–1510 (May 1999). Currently, the resistance of conventional semiconductor devices varies due to the doping means that are used to produce the desired resistance. Thus, the consistent resistance of a nanotube would be of particular value for semiconductor devices. However, neither the form that particular nanotube semiconductor devices would take nor methods for mass production of nanotube semiconductor devices are currently known or available.